Natural silks: archetypal supramolecular assembly of polymer fibres

Major ampullate silk produced by Nephila clavipes spiders exhibits a unique spectrum of desirable mechanical properties. There are useful lessons for materials scientists concerned with the interrelation of synthesis, processing, microstructural design and properties of polymer fibres; lessons learned to date are reviewed briefly. A significant feature of silk spinning in vivo is the evidence that a processable liquid crystalline phase assembles by non-covalent aggregation of polymer (fibroin) having a random coil conformation. It is shown in this paper that the form birefringence calculated for such a liquid crystalline phase is compatible with the measured birefringence of liquid crystalline silk secretion. Also, the linear rate of assembly is estimated for the rod-like aggregates. Comparison with the linear aggregation rate achieved by G-actin (in the well-characterized acrosomal process) confirms that the estimate for fibroin is credible.